Cholic acid, bile salt

See also Bile Acids, Bile Salts, Glycine, Taurine, Glycocholate, Taurocholate, Cholic Acid, Bile Salts and Emulsion of Fats... 

Steroids contain a four-ring structure called the steroid nucleus (Fig. 5.23). Cholesterol is the steroid precursor in human cells from which all of the steroid hormones are synthesized by modifications to the ring or C20 side chain. Although cholesterol is not very water soluble, it is converted to amphipathic water-soluble bile salts such as cholic acid. Bile salts line the surfaces of lipid droplets called micelles in the lumen of the intestine, where they keep the droplets emulsified in the aqueous environment. 

Cholic acid, deoxy-. See Desoxycholic acid Cholic acid, monosodium salt Cholic acid sodium salt. See Ox bile extract Choline alfoscerate. See Glycerophosphocholine Choline bicarbonate CAS 78-73-9 EINECS/ELINCS 201-137-0 Synonyms Hydrogen carbonate 2-Hydroxyethyltrimethyl ammonium Classification Nonaromatic amine Empirical C6H15NO4 Formula (CH3)3NCH2CH20H HCO3 Properties Colorless liq. m.w. 165.19 dens. 

Mammalian bile contains sodium salts of conjugated bile acids, e.g. glycocholic acid and taurocholic acid, in which cholic acid is combined (amide linkage) with glycine and taurine respectively. 

A significant fraction of the body s cholesterol is used to form bile acids Oxidation m the liver removes a portion of the CsHi7 side chain and additional hydroxyl groups are intro duced at various positions on the steroid nucleus Cholic acid is the most abundant of the bile acids In the form of certain amide derivatives called bile salts, of which sodium tau rocholate is one example bile acids act as emulsifying agents to aid the digestion of fats... 

The structure of cholic acid helps us understand how bile salts such as sodium tauro cholate promote the transport of lipids through a water rich environment The bot tom face of the molecule bears all of the polar groups and the top face is exclusively hydrocarbon like Bile salts emulsify fats by forming micelles m which the fats are on the inside and the bile salts are on the outside The hydrophobic face of the bile salt associates with the fat that is inside the micelle the hydrophilic face is m contact with water on the outside... 

Bile acids, which exist mainly as bile salts, are polar carboxylic acid derivatives of cholesterol that are important in the digestion of food, especially the solubilization of ingested fats. The Na and salts of glycocholic acid and tauro-cholic acid are the principal bile salts (Ligure 25.41). Glycocholate and tauro-cholate are conjugates of cholic acid with glycine and taurine, respectively. 

FIGURE 25.41 Cholic acid, a bile salt, is synthesized from cholesterol via 7o -hydroxy-cholesterol. Conjugation with taurine or glycine produces taurocholic acid and glycocholic acid, respectively. Taurocholate and glycocholate are freely water-soluble and are highly effective detergents. 

Bile salt export pump (BSEP gene symbol ABCB11) mediates the biliary excretion of nonconjugated bile salts, such as taurocholic acid, glycocholic acid and cholic acid, and therefore is responsible for the formation of the bile acid-dependent bile flow [97, 98]. Its hereditary defect results in the acquisition of PFIC2, a potentially lethal disease which requires liver transplantation [17, 81, 82, 99]. As discussed in Section 12.5.2, the inhibition of BSEP following drug administration may result in cholestasis. 

Certain compounds are known to achieve higher absorption rates from the GI tract if they are taken with food, and this observation has been linked to their solubilization by bile salts [74], Bile salts, especially those of cholic and deoxycholic acids, have been used to solubilize steroid hormones [75], antibiotics [76], and nonsteroidal antiinflammatory drugs [77]. For example, amphotericin B (an antifungal agent) has been solubilized for parenteral use in micelles composed of sodium desoxycholate [78], As illustrated in Fig. 11, the degree of solubilization of carbamazepine by sodium desoxycholate is minimal below the critical micelle concentration but increases rapidly above this value [79]. At sufficiently high concentrations, when the micelles become saturated in carb-amezepine, the apparent solubility reaches a limiting value approximately seven times the true aqueous solubility in the absence of desoxycholate. 

A somewhat similar situation is provided by the salt of bile acids such as cholic acid [8] or deoxycholic acid [9] (Small, 1968 Cordes and Gitler, 1973 Oakenfull and Fisher, 1977). The hydrophilic and hydrophobic portions of... 

The broad-spectrum antibiotic chlorotetracycline and the aminoglycoside antibiotic kanamycin are observed to lower the cholesterol levels by forming salts with bile acids (e.g.. cholic acid, deoxycholic acid and chenodeoxycholic acid) in the intestinal canal,... 

The aggregation behavior of C21-DA salt in dilute electrolyte medium appears to resemble that of certain polyhydroxy bile salts (25,16). That C21-DA, with a structure quite different from bile acids, should possess solution properties similar to, e.g., cholic acid is not entirely surprising in light of recent conductivity and surface tension measurements on purified (i.e., essentially monocarboxylate free) disodium salt aqueous solutions, and of film balance studies on acidic substrates (IX) The data in Figure 3 suggest that C21-DA salt micelles Incorporate detergents - up to an approximate weight fraction of 0.5 -much like cholate Incorporates lecithin or soluble... 

Figure 4.14 Structures of cholic and chenodeoxycholic acids which are the acids that form the bile salt The asterisk indicates the position at which an ester bond is formed with taurine or glycine so that bile salts are taurocholate, chenodeoxytaurocholate, gly-cocholate, and glycochenodeoxycholate are formed. The structure of taurine is H2NCH2CH2SO3 and glycine is H2NCH2COOH.

J. P. Cruse, M. R. Lewin and C. G. Clark, The effects of cholic acid and bile salt binding agents on 1,2-dimethylhydrazine-induced colon carcinogenesis in the rat. Carcinogenesis, 1981, 2, 439. 

Cholic acid and chenodeoxycholic acid, known as the primary bile acids, are quantitatively the most important metabolites of cholesterol. After being biosynthesized, they are mostly activated with coenzyme A and then conjugated with glycine or the non-pro-teinogenic amino acid taurine (see p. 62). The acid amides formed in this way are known as conjugated bile acids or bile salts. They are even more amphipathic than the primary products. 

Bile salts are exclusively synthesized in the liver (see A). The slowest step in their biosynthesis is hydroxylation at position 7 by a 7-a-hydroxylase. Cholic acid and other bile acids inhibit this reaction (end-product inhibition). In this way, the bile acids present in the liver regulate the rate of cholesterol utilization. 

Bacteria in the intestine can remove glycine and taurine from bile salts, regenerating bile acids. They can also convert some of the primary bile acids into "secondary" bile acids by removing a hydroxyl group, producing deoxycholic acid from cholic acid and lithocholic acid from chenodeoxycholic acid (Figure 18.11). 

Part of the cholesterol newly synthesized in the liver is excreted into bile in a free non-esterified state (in constant, amount). Cholesteiol in bile is normally complexed with bile salts to form soluble cholic acids, Free cholesterol is not readily soluble and with bile stasis or decreased bile salt concentration may precipitate as gallstones. Most common gallstones are built of alternating layers of cholesterol and calcium bilirubin and consist mainly (80-90%) of cholesterol. Normally. 80% of hepatic cholesterol arising from blood or lymph is metabolized to cholic acids and is eventually excreted into the bile in the form of bile salts. 

Conversion of a cholic acid into glycocholate. Glycocholate is an example of a bile salt. The bile salts solubilize lipids in the small intestine so they can be degraded by lipases. 

Salts of cholic acid and its derivatives are known as bile salts. Bile salts are unlike traditional surfactants in that they are rigid and have multiple polar moieties on one side of the molecule thus exhibiting surface activity. 

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